Susac Syndrome1, 2, 10-15 is an extremely rare (1 in 6 million) autoimmune disease which attacks the smallest blood vessels in the cochlea, retina, and brain, causing these vessels to become blocked. This decreased blood flow causes damage to the cochlea resulting in what often appears to be low frequency hearing loss; however we at The Hearing Blog believe that this hearing loss is, in at least some cases, undiagnosed auditory neuropathy spectrum disorder (ANSD), which requires different management and treatment3 than conventional reverse slope sensorineural hearing loss (RSHL).
As many of our readers know, your humble editor manages both the 600+ member Reverse Slope Hearing LossA and 900+ member Auditory Neuropathy Spectrum DisorderB special interest groups on Facebook, so we get to see many interesting things posted in both groups — And a lot of crossover between these groups. For instance, back in late 2011 we uncovered a veritable rats’ nest of previously-undiagnosed ANSD in adults, with now about 10 Members already having received their CI’s …And the 11th & 12th are on track for their CI’s in the next few weeks.
As it turns out, although not that many people who have reverse slope audiograms indeed have ANSD, it appears that a preponderance of ANSD sufferers have pseudo thresholds C such that when the X‘s and O‘s are plotted on the pure tone audiogram, it’s almost meaningless (Berlin et al, 20102), as the unsynchronized “sensation” perceived in the auditory cortex by the patient contains little — If any actual — speech information.3, 4, 5
Note: Lack of the clinician’s recognition of the disconnect between audiometric (pseudo) thresholds and ability of the unsynchronized neural firing signals received at the dorsal cochlear nucleus often leads to mis-diagnosis of the severity of ANSD present, as it’s .NOT. the presence of these scrambled signals recorded on the pure tone audiogram, but the information content these scrambled signals convey.
The “back story” on the Susac’s & RSHL puzzle:
About a year ago, a Susac patient joined the Reverse Slope Hearing Loss group; and when she introduced herself mentioned she had the syndrome. A quick phone call to Dr Google indicated she was one of only about 55 patients in the US — About 1 in 6 million — who had this oddball pathology, so we wrote back to her the routine counseling to be tested for ANSD, and if possible map out any low frequency cochlear dead zones using the TEN test6 so her hearing aids could be fine tuned, yada yada yada…
A few days later, a second Susac patient joined the group; and when she identified as having this extraordinarily rare pathology who also has poor speech discrimination in quiet, it made us sit up and say, “Whoa!” Time to look into this nasty syndrome to find out if the differential diagnosis for this pathology should include ANSD masquerading as RSHL (HINT: We believe it should).
The next step was to use social media to reach out to the 55 or so American Susac sufferers, plus the dozen or so in UK, and elsewhere as they pop up, to determine exactly what type of hearing impairment they actually have, with them contacting their audiologist to perform additional testing if necessary, as laid out below.
We also reached out to a colleague (TM) who co-authored the seminal article on ANSD in reference 3 below to get his take, and he concurred that it could indeed be ANSD, writing back:
I’ve looked in the literature and cannot find an article where the audiology work would be appropriate to diagnose ANSD. Most papers indicate the pure tone or speech loss but I didn’t see any clear electrophysiology. I don’t see why some patients with Susac syndrome couldn’t develop a pattern of ANSD. If the cochlear blood flow is impaired, it is likely that the inner hair cells will not function properly anymore. What is unclear to me is can the outer hair cells be preserved for a while? [Italics added: Ed.] In summary, I think clinicians didn’t really look at the specificity of the hearing loss with MEMR,[5: Ed.] OAE’s, and ABR recordings.
The literature is usually showing that the hearing loss is not reversible, but again there might be some cases where it is. There is also a report from a successful cochlear implantation.
I’ve never seen such patients since I’m exclusively working with children and the syndrome has a late onset. [snip]
Looks like we may be on to something here…
Where we are now:
We at The Hearing Blog are still at the We Don’t Know stage of our Susac/ANSD investigation, due (fortunately) to the dearth of Susac’s patients. However, this also raises the question of should either/or reverse slope audiograms &/or ANSD be a part of the differential diagnosis for Susac Syndrome? If, as TM pointed out above, it’s an issue of cochlear blood flow, then will this lead to expanding the knowledge base for this rare pathology?
Also, we can say that for the confirmed ANSD subset of this already miniscule group of patients that CI’s indeed work to restore hearing, by resynchronizing the neural firing received at the dorsal cochlear nucleus, hence restoring functional communication.
We recommend to clinicians seeing a Susac patient to at bare minimum map out any cochlear dead zones6 for improved hearing aid performance; and more importantly screen for ANSD by measuring acoustic (stapedial) reflex thresholds across the speech range, with canal volume compensated thresholds5, 3 above 90 dBHL as well as absent treated as abnormal; and confirming the diagnosis with the special ABR using alternating high level compression & rarefaction clicks to cancel out the cochlear microphonic artifact; or in other words perform the CI candidacy test battery.7, 8, 9 Also, to further the Susac knowledge base, we recommend measuring inner hair cell integrity with an electrocochleogram (ECochG); and if a trans-tympanic ECochG is performed using a ball electrode placed on the round window, also measuring auditory nerve integrity with an electrical ABR (eABR).
Finally, we remind the reader that although outer hair cell integrity as measured by OAE’s is important, OHC integrity is not part of the differential diagnosis for ANSD.3, 4
How to help our investigation if you have Susac Syndrome:
There is now a special Susac Syndrome + Hearing Loss group where this connection is discussed, with membership restricted to Susac patients and hearing care professionals
- Susac Syndrome – Summary on the Cleveland Clinic website. Note the extensive list of journal references;
- Susac Syndrome on the Cleveland Clinic website;
- Multi-site diagnosis and management of 260 patients with Auditory Neuropathy-Dys-synchrony (Auditory Neuropathy Spectrum Disorder), by Berlin, Hood, Russell, Morlet et al (2010)
- Interview with Charles Berlin, PhD: Auditory Neuropathy Spectrum Disorder, OAEs, ABR, and More
- Acoustic Middle Ear Reflexes: Simple, Underused, and Critically Important [Note the compensation values in Table 2!];
- Threshold Equalizing Noise (“TEN”) test, by Prof Brian CJ Moore, Cambridge University Auditory Perception Lab;
- Gifford, René H PhD: Who is a cochlear implant candidate? Hearing Journal June 2011 – Volume 64 – Issue 6 – pp 16,18-22
- Qualifying For Cochlear Implants: Were YOU Washed Out Due To Improper Speech Testing? The Hearing Blog, December 6, 2013
- Let’s not cause further confusion between ANSD and (C)APD The Hearing Blog, September 19, 2014
- Susac, JO. Editorial: Susac’s Syndrome. Am J Neuroradiology 2004 25:351-352. www.ajnr.org Accessed 3/15/2015;
- Rennebohm R, Susac JO, Egan RA, Daroff RB. Susac’s Syndrome–update. J Neurol Sci 2010 Dec 15;299(1-2):86-91. Epub 2010 Sep 19. PMID: 20855088 [PubMed – indexed for MEDLINE]
- Rennebohm RM, Egan RA, Susac JO. Treatment of Susac’s Syndrome. Curr Treat Options Neurol. 2008 Jan;10(1):67-74. PMID: 18325301
- Genetic and Rare Diseases Information Center (GARD). Susac syndrome. rarediseases.info.nih.gov Accessed 3/15/2015;;
- Susac JO, Egan RA, Rennebohm RM, Lubow M. Susac’s syndrome: 1975-2005 microangiopathy/autoimmune endotheliopathy. J Neurol Sci 2007 Jun 15;257(1-2):270-2. Epub 2007 Feb 28. Review. PMID: 17331544 [PubMed – indexed for MEDLINE] [PubMed]
- Rennebohm RM, Susac JO. Treatment of Susac’s syndrome. J Neurol Sci 2007 Jun 15;257(1-2):215-20. Epub 2007 Feb 26. Review. PMID: 17324441 [PubMed – indexed for MEDLINE]
(A) The original Reverse Slope Hearing Loss group was started in 2008 and was “lost” by Facebook a year later; however it was quickly reconstituted as the Reverse Slope Hearing Loss (New) group. When you join, be sure to check out the Photo Album and Files sections where over 100 Members have posted their audiologic tests results with discussions in the comments, creating a veritable treasure trove of data. It was from a retrospective analysis of these documents in early 2012 that led to the uncovering of the connection between RSHL and ANSD, which was noted by Chuck Berlin exactly three years ago today (3/16/2015) at the 2012 ANSD Conference in St Pete. Intuitively, this makes sense, even if you don’t consider low frequency cochlear dead zones as being in the auditory dys-synchrony portion of the ANSD “spectrum” (we at The Hearing Blog do so);
(B) It was at the above-mentioned 2012 ANSD Conference in St Pete where we created the Auditory Neuropathy Spectrum Disorder group and quickly signed up dozens of professional attendees. In addition, there is a much smaller Adults with Auditory Neuropathy Spectrum Disorder group; and an infrequently used Auditory Neuropathy Spectrum Disorder group on LinkedIn
(C) It was also at this same 2012 ANSD Conference where your humble editor coined the term pseudo thresholds to describe the X‘s & O‘s jotted on the pure tone audiogram when ANSD is present;
(D) For a truly frightening simulation of what ANSD sounds like to the sufferer, please listen to this sequence of profound, severe, moderate, mild, and then no ANSD samples, created a few years ago at Kresge by Chuck Berlin & his crew, and vetted with several unilateral ANSD patients.
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